Method for reducing test cycle time and for improving measuring accuracy at a leak testing process

ABSTRACT

A method and test chamber for leak testing a container with a substantially flexible wall portion wherein the container is introduced into a test cavity so that the wall portion of the container is spaced from an inner adjacent wall portion of the test cavity with a gap being defined between the wall portion of the cavity and the flexible wall portion of the container. A pressure difference is installed as an initial value between the interior of the container and at least the gap by applying a pressure at least to the gap which is smaller than a pressure inside the container. The flexible wall portion is supported form its exterior side within the test cavity so as to prevent the flexible wall portion from bending outwardly into contact with the wall portion of the test cavity as a result of the pressure difference. The time course of a pressure prevailing within the gap is measured as a leak indicative signal.

RELATED APPLICATION

This application is a continuation-in-part of copending U.S. applicationSer. No. 07/469,398 filed Jan. 24, 1990 now U.S. Pat. No. 5,042,291.

FILED AND BACKGROUND OF THE INVENTION

The present invention relates in general to a method for leak testing ofa container, to a test chamber therefor and to a test machine forin-line testing of such containers. More particularly, the presentinvention is directed to a method for reducing test cycle time and forimproving the measuring accuracy at a leak testing process as well as toa test chamber and to a test machine with reduced test cycle time andimproved measuring accuracy.

Methods for leak testing of containers are known at which a pressuredifference is applied between the interior and the exterior of acontainer to be tested as an initial value for latter measuring.Afterwards, the time course of a pressure value, which is dependent fromthe pressure difference installed as the initial value and from leakageconditions of the container to be tested, is measured, significant forleak conditions of the container under test.

Such a leak testing method is e.g. known from the German laid open printno. 24 47 578. This reference provides for a testing method to test thewelding seam of such container with respect to leakage. Therefore suchcontainers are pressure loaded inside and also outside, through anopening of the container to be tested. There is provided separately atest channel around the welding seam of the container and leakage ismonitored by measuring the time course or timely development of pressurewithin said test channel. This measuring is indicative for the leakageof the welding seam of the open container.

From the German laid open print no. 21 15 563 it is further known totest the seam of containers which are closed by a foil lid. Thereby, thebottom of the container is perforated by means of a needle-like end partof a pressure line, by which the inside of the container is pressurized.By monitoring the time course of the inside pressure of the container,an indication is provided indicative of tightness of the container.

From the article "Lecksuche mittels Differenzdruck-messungen" from J. T.Furness, VFI 4/78, it is generally known to test a container on leakageby monitoring its internal or its external pressure. Thereby it isdescribed that the smaller that a volume is selected wherein the timecourse of pressure is monitored, the more accurate such a measuring willbecome.

There exists a clear need for shortening the time span necessitated fora test cycle of a container on one hand and of improving the accuracy ofsuch tests to be able to detect smallest leakages of such containers.

SUMMARY OF THE INVENTION

It is an object of the present invention to shorten the time spannecessitated to leak test a container and to simultaneously improve themeasuring accuracy for leak detection, thus leading to the possibilityto detect significantly reduced leakages in shorter test time.

According to the present invention, this is achieved by a method forreducing a test cycle time and for improving measuring accuracy at aleak testing process for a container whereby such a leak testing processcomprises installing of a pressure difference between the interior ofthe container and the exterior thereof as an initial value. The leaktesting process further comprises measuring of a time course of apressure value which is dependent from the pressure differencepreviously installed as the said initial value and from leakage of thecontainer under test. Measuring of the said pressure value results in aleak indicative measurement. Reducing of test cycle time andsimultaneously improving measuring accuracy is realized by installingthe pressure difference as the said initial value, in that apredetermined pressure is installed at the exterior of a closedcontainer without its closed integrity being destroyed. As measuring ofthe time course of the said pressure value dependent from the pressuredifference installed and from the container leakage, the time course ofthe pressure of the exterior of the closed container is measured.

Further, the volume of the exterior of the closed container at which thepredetermined pressure is installed and at which the time course of thepressure is measured, is minimalized, in that the invention departs fromthe recognition that, for such closed container testing, one and thesame volume is substantially determining test cycle time and measuringaccuracy and that both may be optimized by minimalizing one and the samevolume, namely said pressurized external volume of the container undertest.

With respect to leak testing of closed and especially of prefilledcontainers within test chambers, it is known to install at the exteriorof such a container either over- or under-pressure, as an initial value,then to shut off the test chamber from overpressure or underpressuresources and then to monitor the pressure course at the remaining volumebetween the interior wall of the test chamber and the containerinstalled therein. The measuring cycle time per container issignificantly dependent from the extent of the said remaining volume,between wall of the test chamber and container therein. The bigger thatsuch a volume is selected, the longer the measuring cycle will last,because loading with overpressure or evacuation will consume the moretime the larger that the said remaining volume is selected.

Further, a leak of a predetermined extent of said container and therespective stream of pressurizing gas from the outside to the inside ofthe container or of gas previously contained in the container to itsoutside - in the case of underpressure at the container outside -, willresult in a smaller detectable pressure change signal the bigger thatthe said remaining volume is selected.

For leakage tests of such closed and especially of filled containers upto now a straightforwards approach was practiced in using cylindric testchambers.

Therefrom, it may be seen that the present invention departs from therecognition that for testing closed containers the same volume, namelythe said remaining volume, is responsible for the extent of themeasuring cycle time as well as for the measuring accuracy and that bythe most simple measure, namely of reducing the said volume, both thesaid criteria are optimized, namely the cycle length is minimized andthe measuring accuracy maximized.

An inventive test chamber with improved test cycle time and measuringaccuracy for a container which has a cross-sectional area diminishingalong the direction of a transverse axis through the container,comprises a closable test cavity for introducing the container; meansfor installing a pressure difference as an initial value between theinside of the container and the remaining volume of the test cavity oncethe container is introduced therein; means for measuring a pressurevalue which is dependent from the pressure difference installed and theleakage of the container, whereby the shape of the cavity is selected tobe at least substantially geometrically similar to the shape of thecontainer, so as to minimize the remaining volume and whereby the meansfor installing and the means for measuring communicate with theremaining volume so as to test a closed container without destroying itsclosed integrity.

By the fact that for a closed container the shape of the test cavity isselected to be at least substantially similar to the shape of thecontainer and thus has an open cross-section area which diminishes alongan axis of the cavity as does the cross-sectional area of the container,a minimal volume difference between the volume of the test cavity andthe volume of the container is realized, and thus a minimal remainingvolume defined as above. For leak testing the said container within saidtest cavity and so as to not destroy its closed integrity, the means forinstalling the pressure difference and the means for monitoring the timecourse of the leak significant pressure signal are connected to theremaining volume between inside of the test cavity and the containerintroduced therein.

Another method of the invention for leak testing a container, closedwith a foil-like lid fixed to a projecting rim of the container,comprises the steps of disposing the closed container into a testreceptacle, supporting the closed container within the receptacle at theprojecting rim on a border area of the receptacle, so as to form a firsttest volume between an inner wall of the receptacle and the wall of thecontainer. The receptacle is sealingly closed with a cover so as toprovide a second test volume between the cover and the foil-like lid ofthe container. The first and second test volumes are connected to form acombined test volume along a predominant part of the container closed bythe lid. A pressure difference between the combined test volume and apressure inside the container is established as an initial value, and apressure prevailing within the combined test volume is monitored as aleak indicative signal.

The means connecting the first and second test volumes to form acombined test volume along a predominant part of the container closed bythe lid in the test chamber of the invention for leak testing acontainer according to the aforementioned method includes a plurality ofspaced grooves extending in the receptacle from the inner wall of thereceptacle and the first test volume to the second test volume at alocation radially outward of the border area of the receptaclesupporting the projecting rim of the container. In this form of the testchamber of the invention, seal means are located between the cover andthe receptacle radially outward of the border area of the receptaclesupporting the projecting rim of the container for sealingly closing thereceptacle together with the cover. In another form of the test chamberof the invention, the cover sealingly closes the receptacle by pressingthe projecting rim of the container between the cover and the borderarea of the receptacle.

The above and other objects of the present invention will become moreapparent as the description proceeds.

DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will be morereadily understood when the following detailed description is consideredin conjunction with the accompanying drawings, in which:

FIG. 1 shows schematically a prior art test chamber and its use for leaktesting of closed and filled containers which containers have adiminishing cross-sectional area seen in direction of a transversecontainer axis,

FIG. 2 shows schematically and in analogue representation to FIG. 1, aninventive test chamber realized according to the inventive method,

FIG. 3 shows schematically in a cross-sectional representation apreferred embodiment of an inventive test chamber for leak testing ofcup shaped containers as of yogurt cups,

FIG. 4 shows a schematic, cross-sectional view of a portion of a testchamber of the invention, which could be used in the test chamber ofFIG. 3, wherein a plurality of grooves connect respective volumes V₁ andV₂ for pressure equalization,

FIG. 5 shows a schematic, cross-sectional view of a portion of a testchamber according to another embodiment of the invention,

FIG. 6 shows a schematic, cross-sectional view of another feature of atest chamber of the invention which can be used in any of the otherembodiments.

DETAILED DESCRIPTION

In FIG. 1 there is schematically shown a test chamber 1 as it is knownalso for leak testing of closed containers 3, which, seen in directionof an axis A of the container, have a diminishing cross-sectional areaF₃. The container 3 is filled with a filling material 5 and is e.g.closed by a covering foil-like lid 7. The foil-like lid 7 is fixed alongits periphery to container 3, e.g. by gluing or welding. Such acontainer may be a plastic material cup being closed by an aluminum foil7.

For leak testing, such containers 3 are introduced into the test chamber1 which then is hermetically closed by means of a cover 11 and a seal13. Between the container 3 and the interior wall of the test chamber,which latter consists of the cover 11 and the chamber receptacle 15,there is defined a remaining volume V_(z) which is pressurized by thetest pressure p_(z) which test pressure is different from the pressureinside the closed container 3.

This is realized, as may be seen schematically from FIG. I, by means ofa pressurizing feed line 17 with a valve 19. After pressurizing theremaining volume V_(z) the valve 19 is closed and the time developmentof the pressure p_(z) within the remaining volume V_(z) is monitored,e.g. with the help of a pressure sensor 21, which is preferably adifference pressure sensor. There is led to one of the pressure inputsof the difference pressure sensor a reference pressure p_(R), to theother of its inputs the pressure p_(z) of the remaining volume V_(z)which is on one hand dependent from the pressure previously installedbefore the valve 19 was shut and from leakage of the container 3.

If, as a testing pressure, a pressure is applied to the remaining volumeV_(z) which is lower than the pressure residing inside the container 3,then a leak of the container 3 will result, after shutting valve 19, ina rising pressure in the remaining volume V_(z) because of the gasexchange stream out of container 3 through the leak of the container 3,into the volume V_(z).

Inversely, a reduction of pressure in the remaining volume V_(z) will beregistered due to a leak of the container 3 if, as a test pressure, aninitial pressure is applied to the remaining volume V_(z) which ishigher than the pressure residing inside the container 3.

To initially apply the test pressure p_(z) to the remaining volume V_(z)as an initial value for testing, a gas volume must be fed to or removedfrom the said remaining volume V_(z) the amount of which being thelarger, the bigger the said remaining volume V_(z).

The amount of gas which has to be fed or removed so as to install thetest pressure p_(z), as an initial value, directly influences the timespan necessitated to reach the test pressure initial value, given adefined power of a pressurizing or evacuation source connected to thefeeding line 17. The smaller that the remaining volume V_(z) isselected, the smaller the time span for reaching a predetermined testpressure p_(z) as said initial value will be.

Further, by a given leak and by a given initial test pressure p_(z), andthus an initial, given pressure difference between pressure in theremaining volume V_(z) and pressure in the interior of the container 3,the amount of gas flowing out of such leak per time unit is defined.Thus, a change of pressure within the remaining volume V_(z) as a resultof leakage will become the bigger, the smaller that the said remainingvolume V_(z) is.

To optimally exploit these conditions as schematically shown in FIG. 2,the test chamber is tailored so that it defines together with anintroduced container 3 to be tested, an optimally small remaining volumeV_(z).

The inventive test chamber 31, shown schematically in FIG. 2, comprisesa one side open receptacle 35 with an opening 34, wherebycross-sectional areas F₃₅ of the receptacle 35, seen from the opening34, continuously diminish. The diminution of the cross-sectional areaF₃₅ along the axis A₃₅ preferably accords to the diminution of thecross-sectional area F₃ of a container 3 to be tested and to betherefore introduced into the test chamber 31. Thus, the wall of thecontainer 3 and the inside wall of the test chamber 31 will besubstantially equidistant, once such a container 3 is introduced intothe test chamber 31. Thus, the remaining volume V_(z) is minimalized.

The inventive test chamber 31 comprises a cover 33 which sealinglycloses with schematically shown seals 37 the test chamber 31 after acontainer 3 to be tested has been introduced therein. Application of theinitial test pressure and monitoring the time course of pressure at theremaining volume V_(z) is realized the same way as was described forprior art test chambers and methods according to FIG. 1.

In FIG. 3 there is shown a preferred embodiment of an inventive testchamber again schematically. As an example it is constructed for testingclosed containers 3 of substantial truncated cone form, as for testingyogurt cups, with respect to leakage.

A container 3 to be tested and with a covering lid 7 is shown in dashedlines. The inventive test chamber comprises a receptacle 39 which isformed according to the outside form of the container 3. Thecross-sectional area of the receptacle 39, F₃₉ diminishes in directionof the central axis A substantially cone-like departing from areceptacle opening 41, towards the bottom 43 of the receptacle 39 anddefines a cavity which is substantially similar in the sense ofgeometric similarity with the container 3, so that, when the container 3to be tested is introduced, there are defined between its wall and theinside wall of the receptacle 39 substantially constant distances.

Adjacent to the opening 41 of the receptacle 39 there is preferablyprovided a positioning groove for a collar which is usually provided atsuch containers to which collar the covering foil-like lid of thecontainer is welded (not shown).

The test chamber further comprises a cover 45 which is movingly drivenas shown by reference P and is moved towards or from the receptacle 39,so as to either sealingly close it with the help of the seals 43 or toopen it.

At the bottom of the receptacle 39 there is provided an axially movableand controllably driven piston 47 which is retracted, when a container 3is to be tested is introduced in the test chamber and during the testingof the container, and which, after opening the cover 45, is driven intothe test chamber, so as to eject the tested container 3. The piston 47comprises an enlarged piston head.

At the bottom of the receptacle 39, adjacent to the piston head, a drainsleeve 49 enters into the test chamber which is sealingly closed bymeans of the head of the piston 47 by means of seals 51, once the piston47 is retracted. Thus, after testing a container 3 which was leaking, sothat material contained in the container 3 could possibly penetrate intothe test chamber, the test chamber may be rinsed after the piston 47 hasbeen driven into the test chamber 31 to eject the leaking container 3.Thus, the test chamber 31 is rinsed and the rinsing liquid will bedrained out of the open drain sleeve 49. For further improving rinsingof the test chamber, there may be provided, as at the cover 45, arinsing liquid feed line, possibly with a nozzle arrangement, to ejectrinsing liquid into the test chamber (not shown).

Preferably, and especially for use with containers which are closed bymeans of a covering foil 7, as yogurt cups etc., the test chamber is soarranged that its opening 41 points upwards, By this one prevents thatfilling material within container 3 drops on the covering lid whichcould lead to deterioration of leak testing and especially leak testingof the weld seam between covering lid 7 and the wall of the container,because the lid 7 would then be loaded by filling material to acondition not nominal.

The test chamber according to FIG. 3 comprises, as again schematicallyshown, pressure feed and pressure monitoring means as were described inconnection with FIG. 1 and 2.

For leak testing of containers, as of yogurt-, cream- etc. cups,continuously in line with filling and closing operations for suchcontainers, by which leak testing e.g. every container of the productionshall be tested, a multitude of inventive test chambers, one of whichhaving been described with the help of FIG. 3, are combined to form atest machine. In such a machine the multitude of test chambers accordingto FIG. 3 are preferably arranged on a turnably driven carousel table(not shown), so that, in line with filling and closing of thecontainers, all of them are pressure leak tested before these containersare stored ready for package. Especially for testing of containers witha flexible wall by means of applying under-pressure, areas of thecontainer walls may be pressed on the inner wall of the test chamber. Toprevent this it may be advisable to provide a mesh inlay along andslightly distant from the wall of the test chamber, so e.g. in the formof a cone-shaped mesh inlay which is open at its bottom end and in whichthe container 3 to be tested is introduced. Such a mesh inlaymechanically stabilizes the wall of the container 3 with respect tooutwards bending. Thus, with the help of such a mesh inlay it isprevented that the flexible container wall is bent so as to tightlyreside on the inner wall of the test chamber when under-pressure is usedas a test pressure in the remaining volume V_(z). Possibly pressureequalizing connections are provided between the lower part of thereceptacle 39 and the upper part adjacent to the cover 41 to ensurepressure equalization all around a container 3 to be tested, if a coverof the container tends to sealingly separate the lower part volume ofthe test chamber from the said upper part volume.

Such connections between lower and upper parts of the test chamber toprovide for equalization of the pressure may be provided by appropriategrooves at the cover region of the test chamber, linking the lower partof the remaining volume V_(z) with the upper part V'_(z) thereof.

Thus, providing a receptacle, the open cross-sectional area thereofdiminishing in direction towards the bottom of the receptacle andcomprising a cover for tightly closing, there is realized a most simpletest chamber, from which a container 3, once tested, may be removedwithout any problems.

It must be pointed out that the above described provision of a grid ormesh structured inlay into the test chamber may also prevent amechanically deformed wall of a container under test to sealingly shuteither an evacuation line for installing the initial test pressure andbutting into the remaining volume V_(z) or a measuring line forafterwards monitoring the time development of the pressure within theremaining volume.

Additionally, such a mechanical deformation of the container wall couldlead to leakage of containers which would not occur if such adeformation is prevented as by the said mesh inlay.

In FIG. 4 there is shown an enlarged view of a test chamber which couldbe employed in the apparatus of FIG. 3, for example. The test chamber ofFIG. 4 comprises a receptacle 100 containing a container 101 coveredwith a foil-like cover 103 which is, e.g., glued to a radiallyprojecting rim portion 104 of the container 101, as is known, e.g., fromyoghurt containers. The rim portion 104 is supported on the border of acavity defined within receptacle 100. The cavity defines, with respectto a flexible wall 106 of the container, a first test volume V₁. Thisvolume V₁ is connected to a line 108 to apply pressure. A cover 109closes the cavity of receptacle 100 and forms a second test volume V₂over the container 101, so that the volumes V₁ and V₂ are interconnectedby bypassing pressure connections 110 in the form of a plurality ofspaced grooves. A cone-shaped mesh inlay 112, shown in dotted line, isprovided for use with a pressure in the test volume, smaller than thatwithin the container. The mesh inlay 112 is open at its bottom end andslightly distant from the wall of the test chamber. The mesh inlaystabilizes the flexible wall 106 of the container with respect tooutwards bending as discussed above in reference to FIG. 3.

Another embodiment of the present invention is shown in FIG. 5 wheresealing of the cover 109 with respect to the cavity defined withinreceptacle 100 is not performed by a special sealing as sealing ring 114of FIG. 4, but is provided by pressurizing the rim portion 104 betweenthe cover 109 and the border of receptacle 100. Thus, in this embodimentsmall sealing rings 116 are provided to just seal respective connectinglines 118 communicating the respective volumes V₁ and V₂. Thisembodiment could also be used upside down.

By the technique illustrated in FIG. 6 it becomes possible to surroundthe complete container to be tested by test volume and test pressurewithout any standing area for such container blocking a portion of thecontainer. Thus, in a more general view, it would suffice to deposit thecontainer to be tested at distinct points 120, as schematically shown inFIG. 6, to allow all around pressurizing. This feature of the testchamber and method of the invention could be employed with the meshinlay of previous embodiments to stabilize the flexible side wall of thecontainer.

I claim:
 1. A method for leak testing a container, closed with afoil-like lid fixed to a projecting rim of said container, comprisingthe steps ofdisposing said closed container into a test receptacle,supporting said closed container within said receptacle at saidprojecting rim on a border area of said receptacle, so as to form afirst test volume between an inner wall of said receptacle and the wallof said container, sealingly closing said receptacle with a cover andproviding a second test volume between said cover and said foil-likelid, connecting said first and second test volumes to form a combinedtest volume along a predominant part of said container closed by saidlid, establishing a pressure difference between said combined testvolume and a pressure inside said container as an initial value, andmonitoring a pressure prevailing within said combined test volume as aleak indicative signal.
 2. The method according to claim 1, saidcontainer has a substantially flexible wall portion and including thestep of supporting at least a portion of the flexible wall portion ofthe container from its exterior side within said test receptacle so asto prevent said flexible wall from bending outwardly into contact with awall of the test receptacle as a result of said pressure difference. 3.The method according to claim 2, wherein a mesh inlay is used at leastalong parts of the test receptacle for said supporting of the flexiblewall portion.
 4. The method according to claim 2, including supportingthe flexible wall portion of the container at a multitude of locationsdistributed along the flexible wall portion.
 5. The method according toclaim 1, including minimizing the volume of a gap defined between a wallof the test receptacle and a wall of the container therein to reduce atime amount of establishing said pressure difference and for improvingsensitivity of said monitoring.
 6. The method according to claim 1,including pressurizing the projecting rim of the container between theborder area of the receptacle and the cover for sealingly closing thereceptacle.
 7. A test chamber for leak testing a container, closed witha foil-like lid fixed to a projecting rim of said container, comprisingaclosable test receptacle with an inner wall within which said closedcontainer to be leak tested can be disposed with said projecting rim ofthe container being supported by a border area of said receptacle, so asto form a first test volume between said inner wall of the receptacleand the wall of said container, a cover for sealingly closing saidreceptacle and providing a second test volume between said cover andsaid foil-like lid of the container disposed within said receptacle,means connecting said first and second test volumes to form a combinedtest volume along a predominant part of said container closed by saidlid, means for establishing a pressure difference between said combinedtest volume and a pressure inside said container as an initial value,and means for monitoring a pressure prevailing within said combined testvolume as a leak indicative signal.
 8. The test chamber according toclaim 7, including seal means located between said cover and saidreceptacle radially outward of said border area of the receptaclesupporting said projecting rim of the container for sealingly closingsaid receptacle together with said cover.
 9. The test chamber accordingto claim 8, wherein said means connecting said first and second testvolumes includes a plurality of spaced grooves extending in saidreceptacle from said inner wall of the receptacle and said first testvolume to said second test volume at a location radially outward of saidborder area of the receptacle supporting said projecting rim of thecontainer.
 10. The test chamber according to claim 7, wherein said coversealingly closes said receptacle by pressing said projecting rim of thecontainer between said cover and said border area of the receptacle. 11.The test chamber according to claim 7, further comprising a sealinglyclosable drain sleeve departing from said inner wall of said testreceptacle for removing a rinsing fluid from said closable testreceptacle.
 12. The test chamber according to claim 11, furthercomprising an ejection piston drivably movable from the bottom wall ofthe test receptacle to eject a container tested therein, said drainsleeve being sealingly closable by means of said ejection piston. 13.The test chamber according to claim 7, wherein said container has asubstantially flexible wall portion and wherein said test chamberincludes supporting means with at least one supporting surface, saidsupporting surface being spaced from the inner wall of the testreceptacle to prevent a flexible portion of the container wall frombending outwardly into contact with the adjacent portion of the innerwall due to a reduced pressure within said first and second test volumeswith respect to pressure within said closed container.
 14. The testchamber according to claim 13, wherein said supporting means comprises amesh structure.
 15. The test chamber according to claim 13, wherein saidsupporting means comprises a mesh structure which has a form such that acontainer can be introduced into the mesh structure for mechanicallystabilizing the container with respect to outward bending due to areduced pressure within said first and second test volumes with respectto pressure within said closed container.
 16. A test chamber for leaktesting a container closed with a foil-like lid fixed to a projectingrim of the container, comprising a closable test receptacle with aninner wall within which said closed container to be leak tested can bedisposed so as to form a first test volume between said inner wall ofthe receptacle and the wall of said container, a cover for sealinglyclosing said receptacle and providing a second test volume between saidcover and said foil-like lid of the container, means connecting saidfirst and second test volumes to form a combined test volume along apredominate part of said container closed by said lid, means forestablishing a pressure difference between said combined test volume anda pressure inside the container as an initial value, means formonitoring a pressure prevailing within the combined test volume as aleak indicative signal, and wherein said test chamber further comprisesmeans for supporting said container within said receptacle at aplurality of distinct, spaced supporting points whereby said combinedtest volume and test pressure extends along a predominate part of thecontainer to be tested.
 17. The test chamber according to claim 16,wherein said container has a cross-sectional area diminishing along thedirection of a transverse axis through the container, and wherein saidreceptacle defines a cavity for receiving said container, the opencross-sectional area of said cavity diminishing in a direction towardthe bottom of said receptacle.
 18. The test chamber according to claim16, wherein said test chamber includes a mesh inlay for supporting aflexible wall portion of the container from its exterior side withinsaid receptacle so as to prevent said flexible wall portion from bendingoutwardly into contact with said inner wall of the receptacle as aresult of said pressure difference.
 19. The test chamber according toclaim 18, wherein said distinct, spaced supporting points are formed bysaid mesh inlay.